A closed, Rankine cycle power plant is disclosed in each of U.S. Pat. Nos. 3,842,593 and 3,845,628 wherein an organic working fluid is vaporized in a boiler and supplied to a prime mover housed in a hermetically sealed cannister, such power plant being termed hereinafter, a power plant of the type described. Generally, in a power plant of the type described, the prime mover is a turbine that drives a generator producing power. The vapor exhausted from the turbine is passed into a condenser which converts the exhaust vapor into condensate at a lower temperature and pressure than in the boiler. Some of the condensate in the condenser is supplied to the bearings of the turbine/generator and the remainder is returned to the boiler, either directly, if the condenser elevation relative to the boiler is sufficient, or via a pump if the elevation is insufficient.
The cannister is essentially at the condenser pressure by reason of the exhaust conduit from the turbine, and is relatively cool. As a consequence, the cannister acts as a secondary condenser for exhaust vapors present in the cannister, such vapors condensing in the cannister and collecting as a liquid in a sump at the lowest level therein. In addition, leakage of lubricating working fluid from the bearings contributes to the liquid in the bottom of the cannister. To prevent its flooding, the cannister must be provided with a system that will drain liquid working fluid, preferably, as efficiently as possible.
One approach is to elevate the cannister relative to the boiler sufficiently to establish a liquid head that will force the liquid into the boiler. This approach requires no energy, but the price is a power plant that is vertically elongated to provide the necessary liquid head between the cannister and the boiler. Where it is necessary, or desirable, to reduce or to minimize the vertical height of the power plant, this approach is not satisfactory; and in such case, it is conventional to pump the liquid in the cannister into the boiler. The problem here is the extra component represented by the pump and the power expended thereby. In a small, highly reliable power plant, of said 1 Kw rating, any extra component or wasted power will reduce the reliability, efficiency and operating capacity of the system.
Therefore, it is an object of the present invention to provide a method of and apparatus for draining a cannister containing the prime mover of a power plant of the type described, wherein the cannister is drained without adversely affecting the reliability, operating efficiency or capacity of the system.